Chapter 96. Skin Problems in Amputees

In most centers, artificial limbs are constructed in a modular fashion.1 The stump is placed in a thermoplastic socket that is then fitted into the main body of the limb. The bulk of the prosthesis comprises a metal frame with articulations and an outer casing of acrylic resin or carbon composite material. Before fitting the limb, many patients place their stump in a liner designed to reduce friction on the skin. This may be an expanded plastic cup, a silicon/mineral oil sleeve, or a cotton or nylon sock. The prosthetic limb, once fitted, is held in position by one of a range of suspension elements. In above-knee (Fig. 96-1) or proximal arm amputations, this is usually a fabric belt arrangement worn around the waist or shoulders, respectively. Below-knee amputees require a different system using either a butyl rubber sleeve or corset to hold the appliance firmly onto the thigh (Fig. 96-2). Many patients with above-knee amputations now use a suction socket device that provides sufficient suspension by holding the prosthesis in place through negative pressure without the need for additional belts (see Fig. 96-1).

Limb prostheses are the subject of continual technological development particularly in the field of bionics. Myoelectric devices, for example, rely on skin contact with electrodes to detect neuromuscular signals that can be converted to artificial limb movement. Neuroprosthetic devices involve implantation of electrodes into neural tissue usually through the skin, for example, cochlear implants. Such devices are under development for prosthetic limbs. These devices thus have the potential for causing skin problems.

The skin of an amputation stump is not designed to withstand the physical insults it encounters within a prosthetic limb. For example, although some adaptation to friction or pressure occurs, some skin problems are inevitable. If these dermatoses cannot be prevented or rapidly resolved by prosthesis adjustment or medical intervention, they can incapacitate the patient, particularly those who have lower limb, weight-bearing prostheses. As a result, patients may suffer social isolation, emotional distress, or even financial deprivation if they are unable to work.

Skin problems may occur because of allergy or chemical irritation to materials in contact with the skin, as well as from trauma and occlusion. Examples of physical stresses on the skin include shearing and friction from elements in the socket and pressure on load-bearing areas, especially on the tibial tuberosity in below-knee amputations and the ischial tuberosity, adductor region, or groin in above-knee amputations. In all cases, the occlusion results in increased humidity from trapped perspiration, increasing the likelihood of irritation, allergy, and infection.

The common skin disorders in amputation stumps can be classified into diseases related to the reasons for the amputation, physical effects of a prosthesis, infection, contact dermatitis, and other cutaneous disorders.

Epidemiology

The great majority of artificial limb wearers are amputees, although a small proportion are people with congenital limb malformations. Lower limb amputees are the most numerous and are also the group at greatest risk of skin problems. Traumatic amputations are possibly more likely to be associated with a dermatosis2 although the commonest problems encountered are the same as for all amputees.3 Modern limb prostheses allow many of today's amputees to lead an active life with good mobility. Nevertheless, as many as 73% of one cohort of lower limb amputees reported at least one skin disorder.2 In a further group of 745 lower leg amputees, 40.7% had at least one skin problem. Further analysis identified four factors independently associated with dermatologic disorders, namely transtibial amputation, employment status, type of walking aid used, and peripheral vascular disease.4 A more recent questionnaire-based study of 805 lower limb amputees5 suggests that the factors more likely to be associated with skin problems are, smoking, younger age, female sex, washing the stump frequently and the use of antibacterial soaps. Overall one-third of amputees, either upper or lower limb, experiences a skin problem that significantly interferes with the normal use of the artificial limb.6

Dermatoses Related to the Reasons for Amputation

Several disorders resulting in the need for amputation can have a significant impact on skin integrity. In general, younger patients require artificial limbs because of traumatic amputations, congenital abnormalities, or malignancy, whereas in the older age group, arterial disease and vascular complications of diabetes mellitus predominate. Amputations after trauma or severe vasculitis may be associated with scarring that makes for a suboptimal prosthesis fit (Fig. 96-3). Stump dermatoses appear to be more likely in patients following traumatic amputations. Koc et al2 found a skin problem in nearly three quarters of amputees most of whom had lost a limb as a consequence of mine explosions. The nature of current conflicts means that, presently, such amputations are unfortunately common amongst both service personnel and civilians. Vasculitis resulting in amputation may be ongoing and cause problems in the skin of amputation stumps (Fig. 96-4). However, it is diabetes mellitus that is particularly associated with protracted skin problems (Chapter 151) as a result of impaired wound healing, susceptibility to infection, abnormal sensory nerve function, and disruption of normal tissue fluid balance.7 Diabetic amputees as a group require more frequent clinical review to prevent complications. Treatment of the diabetic amputee not only requires good control of the blood glucose level but possibly a change of the stump environment through adjustment or redesign of the artificial limb. The diabetic amputee highlights the need for close links with a prosthetics department, which allow rapid referral of patients for assessment.

Physical Dermatoses

The physical effects of wearing a prosthesis are the most common causes of skin problems.6,8 These can be divided into those resulting from repeated direct trauma and those secondary to disturbance of tissue fluid dynamics.

Direct Physical Trauma

Ulceration

Ulceration and callus formation are seen where there is chronic pressure or repeated frictional forces on stump skin. Ulceration may also be caused by infection or poor cutaneous nutrition, particularly secondary to diabetes mellitus (Figs. 96-5 and 96-6). Stump ulcers should be treated early as malignancy may develop in long-standing ulceration.9 With repeated infection and ulceration, an amputation scar on the distal stump skin can erode further. In some cases, the skin may become completely adherent to bone and develop thick, callus-like hyperkeratosis (Fig. 96-7), which may necessitate revision of the distal bony surface. Ulceration or other injuries incurred while putting on artificial limb components may be particularly associated with poor manual dexterity consequent on neurological disorders or arthritic changes.10,11 Incorrect use of some appliance components can also result in injury.12 Patient selection and access to follow-up advice is therefore important in reducing such injuries. Apparently spontaneous ulceration at unexpected sites is occasionally seen (Fig. 96-8). In every instance, the cause of the ulceration must be determined to resolve a chronic process that can become totally disabling. However, a recent study examining 102 patients over 4 years suggests that the majority of patients with delayed wound healing or secondary ulcers will experience healing despite continuing to use their prosthesis, provided they are carefully monitored.13

Physical Dermatitis

In some patients, eczema may be caused by a poorly fitted or misaligned prosthesis or by edema and congestion of the terminal portion of the stump; only with alleviation of these problems does the condition clear.

Epidermoid Cysts and Follicular Keratoses

Epidermoid cysts and follicular keratoses are two ends of a spectrum of the same disorder. Repeated pressure and friction from the prosthesis appears to cause invagination of keratin around hair follicles, which then results in a foreign-body reaction. Follicular keratoses are therefore the earliest changes.14 These are very common, often multiple, and distributed at sites of weight bearing such as the anterior tibial area, popliteal fossa, and the adductor or inguinal areas of the thigh (Fig. 96-9A). Fortunately, they cause little trouble in many cases, but they can become inflamed and painful particularly if the patient picks at them to extract the keratin plug or if they become infected. Inflamed follicular keratoses can have an acneiform appearance, leading some to suggest that they represent a form of acne mechanica. When the continued pressure and friction causes the keratin to extend deeper into the dermis, larger cystic lesions, 1–3 cm in diameter, form; these are commonly termed posttraumatic epidermoid cysts. Meulenbelt et al15 described a case of follicular keratoses of a transfemoral amputation stump in a patient who did wear an appliance at all. These lesions recurred after resection and were associated with retention of vellus hairs. This raises the possibility that, in some individuals, mechanisms other than just friction may be involved. Deeper cysts can be very tender when compressed by the prosthesis. Some cysts have an obvious punctum and patients may express keratinous material from them. Large cysts can be so painful that the patient can no longer wear a weight-bearing prosthesis each day (see Fig. 96-9B and 96-9C). Distention of the overlying epidermis can occur, followed by spontaneous rupture. A serous, purulent, or hemorrhagic fluid is then discharged. The resulting sinus is difficult to occlude and the discharge continues as long as the prosthesis is worn. Intercommunicating sinuses can appear and spontaneous ruptures may occur. In advanced cases, a granulomatous reaction occurs around the cyst with considerable capillary dilation, vascularization, and a heavy inflammatory infiltrate progressing to abscess formation (see Fig. 96-9B).

Management of this condition can be difficult. Clearly, prevention is the ideal but is not always possible despite regular prosthetic assessments. The fit of the prosthesis is the single most important method of preventing cyst formation. The problem can sometimes be improved or successfully eliminated by proper fitting and aligning of the prosthesis and continued adjustment by the prosthetist. Rough surfaces in areas of increased contact pressure in the socket, particularly the suction socket, tend to catch the skin, increasing the shearing forces. For this reason, the lining of the socket should be kept smooth. With the idea of inserting a buffer between the skin and the socket, protective devices such as liners and stump socks are used. Various synthetic films and adhesives, such as Teflon, have been found satisfactory as liners. They allow for a smooth, gliding action of the prosthetic socket wall or brim against the skin. Applying a vapor-permeable adhesive membrane to the skin before fitting the appliance can also help reduce frictional trauma. Topical glucocorticoids can be used at night to reduce inflammation and provide symptomatic relief. Intralesional injection of glucocorticoids into the cysts and their channels also results in temporary improvement.

Surgical intervention is useful in cases with a few lesions that are not infected. Lesions can be surgically incised and drained. In other instances, removal of the prosthesis is sufficient to cause the lesion to involute, provided that the cyst has not become too large. However, spontaneous rupture, incision, and drainage, and even spontaneous resorption of the lesion are of only temporary benefit. When the prosthesis is worn again, these cysts can recur so that surgical excision is not always the treatment of choice, especially in continually rubbed areas.

In selected cases, systemic retinoid therapy may be appropriate to minimize hyperkeratosis. One author found oral isotretinoin to be effective in a patient described as having acne mechanica.16

Disturbances of Tissue Fluid Dynamics

Edema

Amputation of a lower extremity greatly disturbs the normal pattern of blood and lymph channels, as well as the relationship of pressure both inside the vessels and in the surrounding tissues of the stump. An important feature of care during convalescence after amputation is the reduction of edema and stabilization of new circulatory patterns in the stump. Swelling can be partially prevented by gradual compression of the stump tissues with an elastic bandage or “shrinker” sock before fitting the prosthesis and socket.

When an amputee begins to wear a suction-socket prosthesis, the skin must adapt to an entirely new environment. The patient can expect edema, reactive hyperemia for days or weeks, a reddish-brown pigmentation resulting from capillary hemorrhage, and, occasionally, serous exudation and crusting of the skin of the distal portion of the stump. These changes are relatively innocuous, usually short lived, and do not usually require therapy.

The extent to which edema may persist or recur in the healed stump depends on many factors.17 Edematous portions of the skin of the distal part of the stump may become pinched and strangulated within the socket (Fig. 96-10). Such areas may ulcerate if they catch in the spring-valve opening and become gangrenous as a result of the impaired blood supply. Therapy includes eliminating all mechanical factors contributing to the edema, such as choking by the socket, poor fitting, and misalignment. Excessive negative pressure in a suction-socket prosthesis also contributes to circulatory congestion and edema. Treatment should be directed toward better support of the distal soft tissues. Occasional use of an oral diuretic sometimes allows the edema to resolve.

Verrucous Hyperplasia

Verrucous hyperplasia refers to a reactive hyperplastic condition, characterized morphologically by numerous, coalescent warty papules (Fig. 96-11). It occurs when the chronic pressure effects of a poor prosthetic fit disrupt vascular and lymphatic channels, resulting in chronic tissue edema. The same appearance is seen around longstanding leg ulcers where there is an element of lymphedema (see Chapter 174). Histologic examination can show evidence of pseudoepitheliomatous hyperplasia, although the condition itself is benign and potentially reversible. However, in neglected cases, malignant change can occasionally occur (see Fig. 96-11C). Bacterial infection may play a role in the development of pseudoverrucous hyperplasia, as secondary mixed flora infections are common because of the poor superficial blood flow and the convoluted surface (Fig. 96-12). External compression is the best method of treatment, in combination with topical control of bacterial infection. In below-knee amputees, the distal part of the stump is edematous; the stump dangles freely in the socket or has no distal support or partial end-bearing. When the stump end is supported in the socket by a temporary cushion or platform, compression gradually reduces and slowly clears the verrucous condition. The greater the compression on the distal stump, the more immediate and lasting is the improvement. The use of compression bandaging, shrinker socks and other pads, and partial end-bearing all have a definite place in therapy and can be skillfully applied by the prosthetist. Short courses of oral diuretics may be indicated to reduce edema of the stump. The medication can be gradually decreased when the stump and its skin return to normal.

Acroangiodermatitis

Acroangiodermatitis occurs when the chronic pressure changes result in vessel proliferation in the upper- and middermis. There is also extravasation of red blood cells and these features combine to give a purplish hue to the papules and plaques that appear on a background of edematous skin. The appearance may mimic Kaposi sarcoma.18 Some authors suggest that acroangiodermatitis occurs in above-knee amputees who use a suction socket prosthesis that exerts negative pressure.19 However, there are reports of acroangiodermatitis in below-knee amputees,20 and the same condition is seen in chronic venous insufficiency and in the patients with arteriovenous shunts (acroangiodermatitis of Mali). Management of this condition is the same as for stump edema and verrucous hyperplasia.

Bacterial and Fungal Infections

The bacterial flora of amputation stumps have been examined in small groups of patients,21,22 and the most common species encountered are Staphylococcus epidermidis, S. aureus, and Streptococcus sp. (see Chapter 176). The moist, occluded environment under a prosthesis is ideal for fungal and bacterial growth so that minor skin infections occur fairly frequently. In one study, S. aureus folliculitis or Trichophyton rubrum infection was identified in 3% of the study population.6 Infections are more common during hot weather and in those amputees who pay insufficient attention to stump hygiene, partly because in these situations the skin becomes macerated more readily and follicular infections become more likely. Although folliculitis (Fig. 96-13) and furuncles are more common, superficial infections of the skin itself may also occur (see Chapter 176). Superficial dermatophyte and candidal infection (see Chapters 188 and 189) are also common and may be difficult to eradicate because of the ideal environment for fungal growth within a prosthesis.

The diagnosis of infection is usually obvious when the rash extends onto skin not covered by the prosthesis. Underneath the prosthesis, any superficial infection may present as a nonspecific scaling erythema indistinguishable from that caused, for example, by chronic irritation. All stump rashes should be swabbed and scraped for bacterial and fungal culture.

In the management of bacterial infections, oral antibacterial therapy should be directed by bacterial culture and sensitivity. Topical antiseptics or antibacterials can be used but some antiseptic preparations can cause irritation and there is also the potential for sensitization.

Superficial fungal infections respond to appropriate topical therapy (see Chapters 188 and 189) but can be hard to completely eradicate because of the favorable conditions for fungal growth. In this situation, systemic antifungal therapy is useful.

Contact Dermatitis

(See Chapters 13 and 48)

The clinical presentations of irritant and allergic contact dermatitis affecting amputation stumps are indistinguishable (Fig. 96-14), ranging from dry, scaling erythema to weeping dermatitis.6 Indeed, the morphologic features may be the same as nonspecific eczematization where no irritant, allergic, or infectious cause is found, and where there is no history of eczema or atopy. Consequently, a careful history and examination is essential if one is to identify irritant or allergic causes (Table 96-1). This includes accurate timing of the onset of dermatitis in relation to changes in the patient's appliance routine or the composition of the prosthesis. The distribution of rash typically matches the site of the contactant. To identify a primary irritant or allergen, it is particularly important for the dermatologist to observe the patient removing and refitting their limb, making note of its construction and any medicaments or other agents such as cleansers, talcs, and creams that the patient uses. These products may contain allergens such as fragrances or preservatives. Colored stump socks may contain potentially allergenic nylon dyes.

Knowledge of the materials used in prosthesis manufacture is also necessary when considering potential sensitizers and irritants. This is best achieved by liaison with the local prosthetist, as different construction techniques may be used in different areas. In general, modern modular prostheses are fabricated with sockets, liners, and casings that may contain acrylic resins, carbon composites, and thermoplastics. Epoxy and, occasionally, polyester resins are still used by some manufacturers. Acrylate-based thread sealants are commonly used in socket bolts and metalwork. Butyl or black rubber material may be used to conceal access points to the metal frame. Rubber materials can also be found in some suction socket valves (Fig. 96-15). Accelerators used in the manufacture of natural or synthetic rubbers are potential allergens, for example, dialkyl thiourea used in chloroprene rubber.23 Suspension elements often include chrome-tanned leather and sometimes have metal fastenings, rivets, or screws containing nickel. Glues containing para-tertiary butylphenol formaldehyde resins are often used.

Repairs or adjustments to prostheses can introduce new irritants and allergens. For example, sockets sometimes have additional leather linings cemented to points of friction or pressure.

Irritant dermatitis (see eFig. 96-15.1) can be due to occluded contact with volatile solvents in glues or resins and from fragrances and detergents in topical medicaments or lubricants. Soaps and other washing materials used to clean appliances can cause irritation if they are not removed by proper washing (see Table 96-1). Burns from a malfunctioning electrode used in a myoelectric prosthesis have been reported.24

Contact allergy should always be considered as a cause of inflammatory and dermatitic disorders affecting the stump, especially if there is secondary spread (see Table 96-1). In addition to standard series patch testing, the authors recommend an extra series of allergens to include components of plastic, including acrylic, epoxy, and polyester resin systems, as well as an azo dye series. It is important to test with pieces of the prostheses and all materials applied to the stump skin including emollients, cleansers, powders, medicaments, and cosmetics. In our experience, the most common relevant allergens are nickel, acrylates, rubber, chromate (in leather), para-tertiary butylphenol formaldehyde resin, and components of topical applications.6

Other Cutaneous Disorders

Common skin diseases, for example, eczema (see eFig. 96-15.2) and psoriasis (see eFig. 96-15.3), may affect amputation stumps. Those diseases that exhibit the Koebner phenomenon, especially psoriasis or lichen planus, have been reported on amputation stumps with little involvement of other areas of skin. Treatment should always take into account the implications of an occluded environment.

Hyperhidrosis can be a problem in some patients resulting in maceration of the skin increasing the risk of erosions and even ulceration. Standard topical antiperspirants can be irritating under occlusion and one novel approach is to use intradermal botulinum toxin A.25

Benign keratoses, warts, nevi, and a variety of cutaneous papillomas may occur on stump skin and occasionally cause discomfort when a prosthesis is worn. Malignancies have also been described and squamous cell carcinoma (Marjolin's ulcer)9 may develop in nonhealing chronic stump ulcers or verrucous hyperplasia (see Fig. 96-11). The patients who have amputations for lymphangiomas may develop the Stewart–Treves syndrome and metastatic lymphangiosarcoma (see Chapter 128). There is a risk that such malignancies may not be recognized as an ulcer might be wrongly blamed entirely on trauma from a poorly fitting prosthesis. A biopsy of persistently ulcerated areas should be undertaken.

Treatment of these benign and malignant tumors is the same as when they occur elsewhere on the skin. Healing after tumor excision may take weeks, during which time the artificial limb may not be worn.

General Management Considerations

Many of the more common skin problems can be prevented or controlled by adherence to an appropriate hygiene and skin-care regimen in conjunction with regular prosthetics reviews, which ensure that the prosthesis remains appropriate and correctly adjusted. To this end, it is important that good communication exists between the dermatologist and prosthetist, which permits rapid referral of patients before skin disorders become established.

As a general routine, the stump skin should be washed at night rather than in the morning because newly washed skin is hydrated and swollen, thereby increasing the likelihood of friction and shearing trauma. Nonperfumed soap should be used to minimize contact with potential sensitizers and fully removed with tepid water and gentle rubbing with a nonabrasive towel.

Antibacterial soaps and washes can reduce the possibility of infection in addition to their cleansing action. However, these antiseptic preparations can cause irritation or allergy in a small number of cases and patients should be warned about this. If a stump sock is worn, it should be changed daily and washed and rinsed fully as soon as it is taken off, before perspiration is allowed to dry within it. Silicone liners should be washed every day.